1. Field of the Invention
The present invention generally relates to a semiconductor device. More specifically, the present invention relates to a chip-size packaged resin-sealed type semiconductor device including a cooling function, and a method of manufacturing the same.
2. Background Information
In recent years, portable devices represented by notebook PCs, cellular phones, etc. have rapidly become popular, and there are growing demands for much smaller, thinner, and lighter semiconductor devices to be mounted on such portable devices. One key technology which complies with such demands is a high-density packaging technology which includes a CSP (chip size package) and so forth. According to the CSP, the package size can be brought infinitely close to the size of a semiconductor chip. In particular, a W-CSP (wafer level chip size package) is attracting special attention as a product that realizes an ultimate compact package. In the W-CSP, the sealing/molding process is done at a wafer level, and thus the W-CSP is expected to be an effective measure for reducing production costs.
With respect to a high-density packaging technology including the W-CSP, it is necessary to cool the semiconductor chip efficiently without affecting the miniaturization concept that is the essential feature in the high-density packaging technology. For example, a semiconductor device having a cooling function is disclosed in Japanese Patent Application Laid Open No. 2001-291793, pp. 3-4, FIGS. 2 and 3, and Japanese Patent Application Laid Open No. 2003-17638, pp. 3-4, FIG. 1. Japanese Patent Application Laid Open No. 2001-291793 and 2003-17638 are hereby incorporated by reference
The semiconductor device as disclosed in Japanese Patent Application Laid Open No. 2001-291793 has a metal radiating material (i.e. cooling post) provided inside a sealing resin of a CSP, whereby the heat generated from the semiconductor chip can be released naturally through the radiating material.
The semiconductor device as disclosed in Japanese Patent Application Laid Open No. 2003-17638 is a stack type MCP (multi chip package) where a number of semiconductor substrates are stacked to be mounted on a single package. In this stack type MCP, one or more Peltier elements, which are radiating materials, are stacked along with the semiconductor substrates in order to control heat conduction among the substrates. Thereby, even with a laminating structure of a number of semiconductor substrates having different junction temperatures, all the semiconductor substrates can be cooled efficiently.
With respect to high-density packaging technology such as the W-CSP or the like, a part of a semiconductor chip, for example the back surface of the semiconductor chip where a semiconductor element is not formed, is likely to be exposed to air in most cases. The thermal emissivity of silicon exposed to air is about 0.038. This is considerably low compared to the thermal emissivity 0.93 of silicon being sealed in a usual mold package. From here onwards, it is difficult for silicon by itself to radiate heat. However, adopting an external heat radiation fin as in the conventional cases in order to resolve such problems is contrary to the miniaturization concept that is the original purpose in the production of high-density packaging technology, and is not ideal.
The semiconductor device as disclosed in Japanese Patent Application Laid Open No. 2001-291793 radiates heat through the metal radiating material provided inside the sealing resin under a natural convection environment. Therefore, in order to improve the cooling efficiency, it is necessary to enlarge the size of the radiating material. Considering this point, it is difficult to have a semiconductor chip that consumes a great amount of power mounted on the semiconductor device.
The semiconductor device as disclosed in Japanese Patent Application Laid Open No. 2003-17638 forcibly cools down by using the Peltier elements, and therefore, it exhibits better cooling efficiency when compared with the semiconductor device of Japanese Patent Application Laid Open No. 2001-291793. However, in attaching separate Peltier elements to the surface of the semiconductor chip, there is a possibility that air or other particles may enter the junction between the Peltier elements and the semiconductor chip. A layer of such air may prevent conduction of heat, and may deteriorate the heat radiation effect of the Peltier elements.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved semiconductor device and an improved method of manufacturing a semiconductor device. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.